Considering the above-mentioned disadvantages in the case of balance measurement systems of the described kind, an object of the invention is to provide a vibration-type measurement pickup, which can, on the one hand, have flowing through it simultaneously two media, which differ measurably from on another in at least one physical property, for example the mass flow rate, the density of the medium and/or the temperature of the medium, and which, on the other hand, nevertheless has a good zero-point stability.
To achieve this object, the invention resides in a measurement pickup suited for the, especially simultaneous and/or differential, measurement of media flowing in two medium-lines. The measurement pickup includes, for this purpose, at least four measuring tubes for conveying media to be measured. Each of these measuring tubes has a first, inlet end and a second, outlet end, and is made to vibrate, especially simultaneously with the others, at least at times, during operation. The measurement pickup further includes an electromechanical, especially electrodynamic, exciter mechanism for effecting vibration of the measuring tubes, together with a sensor arrangement reacting at least to local vibrations of the measuring tubes for producing at least one measurement signal influenced by vibrations of the measuring tube. In such case, of the at least four measuring tubes, a first measuring tube and a second measuring tube are, at least at times, inserted into the course of a first medium-line in a manner such that each of these two measuring tubes simultaneously conveys a partial volume of a medium flowing through the first medium-line, and, of the at least four measuring tubes, a third measuring tube and a fourth measuring tube are, at least at times, inserted into the course of a second medium-line in a manner such that each of these two measuring tubes simultaneously conveys a partial volume of a medium flowing through the second medium-line.
Additionally, the invention resides in an inline measuring device, which includes the aforementioned measurement pickup, for determining a mass flow rate of a first medium flowing in a first medium-line and a mass flow rate of a second medium flowing in a second medium-line and/or for determining a balance between the first mass flow rate of the first medium and the mass flow rate of the second medium.
A basic idea of the invention is that, on the one hand, the first medium instantaneously located in the measuring tubes, as well as the second medium instantaneously located in the measuring tubes, are each split into partial volumes which are essentially the same size, and that, on the other hand, the two partial volumes of the first medium, as well as also the two partial volumes of the second medium are each arranged, among themselves, symmetrically with respect to an imaginary centerline of mass, or centerline, of the measurement pickup. Stated differently, such concerns dividing the mass flow of the first medium to be measured and the mass flow of the second medium to be measured, in each case, into two essentially equally large flow portions and conducting the flow portions so through the measurement pickup, that, even in the case of media of physical properties deviating from one another, an essentially symmetric distribution of the relevant physical properties, such as e.g. mass flow rate, density, viscosity, temperature, etc. is maintained with respect to the aforementioned centerline.
An advantage of the measurement pickup of the invention is, among other things, that, in spite of the fact that it can be manufactured comparatively cost-favorably, it nevertheless exhibits a very high accuracy of measurement, especially also a very high zero-point stability.